Air-fuel ratio sensor is used to detect a ratio of excess air in the exhaust gas of the internal-combustion engine, and various techniques have been proposed for the detection of abnormality of such air-fuel ratio sensor. For example, according to a technique disclosed in a patent document 1, Japanese Patent Laid-Open No. 2010-256233 (patent document 1), a Central Processing Unit (CPU) is configured to detect abnormality of a sensor element based on an air-fuel (A/F) detection voltage, and a terminal voltage of a sensor.
According to the technique of the patent document 1, an abnormality in a sensor control is identifiable. However, according to the technique of the patent document 1, even though it is distinctively/distinguishably determinable whether a short-circuit occurs as (i) an inter-terminal short-circuit as to two terminals of an air-fuel ratio sensor, or (ii) a battery voltage (VB) short-circuit as to one or both of two terminals of the air-fuel ratio sensor short-circuiting to a power source, which one of an upstream terminal or a downstream terminal is short-circuiting to a power source or to a ground is not determinable.
More practically, the technique in the patent document 1 cannot tell which one of a plus terminal or a minus terminal has a short circuit to a power supply or a ground failure, because, in both of a power source short-circuit case and a ground short-circuit case, a voltage of both of the plus and minus terminals adheres to a ground voltage, making it difficult to distinguish one from the other.